FGF19 signaling cascade suppresses APOA gene expression

AMPK signaling pathway regulated the expression of the ApoA1 gene via the transcription factor Egr1 during G. parasuis stimulation

Glaesserella parasuis (G. parasuis) is the causative agent of porcine Glässer's disease, resulting in high mortality rates in pigs due to excessive inflammation-induced tissue damage. Previous studies investigating the protective effects of G. parasuis vaccination indicated a possible role of ApoA1 in reflecting disease progression following G. parasuis infection. However, the mechanisms of ApoA1 expression and its role in these infections are not well understood. In this investigation, newborn porcine tracheal (NPTr) epithelial cells infected with G. parasuis were used to elucidate the molecular mechanism and role of ApoA1. The study revealed that the AMPK pathway activation inhibited ApoA1 expression in NPTr cells infected with G. parasuis for the first time. Furthermore, Egr1 was identified as a core transcription factor regulating ApoA1 expression using a CRISPR/Cas9-based system. Importantly, it was discovered that APOA1 protein significantly reduced apoptosis, pyroptosis, necroptosis, and inflammatory factors induced by G. parasuis in vivo. These findings not only enhance our understanding of ApoA1 in response to bacterial infections but also highlight its potential in mitigating tissue damage caused by G. parasuis infection.

Metabolic Effect of Blocking Sodium-Taurocholate Co-Transporting Polypeptide in Hypercholesterolemic Humans with a Twelve-Week Course of Bulevirtide-An Exploratory Phase I Clinical Trial

Bile acids (BA) play an important role in cholesterol metabolism and possess further beneficial metabolic effects as signalling molecules. Blocking the hepatocellular uptake of BA via sodium-taurocholate co-transporting polypeptide (NTCP) with the first-in-class drug bulevirtide, we expected to observe a decrease in plasma LDL cholesterol. In this exploratory phase I clinical trial, volunteers with LDL cholesterol > 130 mg/dL but without overt atherosclerotic disease were included. Thirteen participants received bulevirtide 5 mg/d subcutaneously for 12 weeks. The primary aim was to estimate the change in LDL cholesterol after 12 weeks. Secondary endpoints included changes in total cholesterol, HDL cholesterol, lipoprotein(a), inflammatory biomarkers, and glucose after 12 weeks. In addition, cardiac magnetic resonance imaging (CMR) was performed at four time points. BA were measured as biomarkers of the inhibition of hepatocellular uptake. After 12 weeks, LDL cholesterol decreased not statistically significantly by 19.6 mg/dL [−41.8; 2.85] (Hodges−Lehmann estimator with 95% confidence interval). HDL cholesterol showed a significant increase by 5.5 mg/dL [1.00; 10.50]. Lipoprotein(a) decreased by 1.87 mg/dL [−7.65; 0]. Inflammatory biomarkers, glucose, and cardiac function were unchanged. Pre-dose total BA increased nearly five-fold (from 2026 nmol/L ± 2158 (mean ± SD) at baseline to 9922 nmol/L ± 7357 after 12 weeks of treatment). Bulevirtide was generally well tolerated, with most adverse events being administration site reactions. The exploratory nature of the trial with a limited number of participants allows the estimation of potential effects, which are crucial for future pharmacological research on bile acid metabolism in humans.

Understanding the ins and outs of lipoprotein (a) metabolism

PURPOSE OF REVIEW

This review summarizes our current understanding of the processes of apolipoprotein(a) secretion, assembly of the Lp(a) particle and removal of Lp(a) from the circulation. We also identify existing knowledge gaps that need to be addressed in future studies.

RECENT FINDINGS

The Lp(a) particle is assembled in two steps: a noncovalent, lysine-dependent interaction of apo(a) with apoB-100 inside hepatocytes, followed by extracellular covalent association between these two molecules to form circulating apo(a).The production rate of Lp(a) is primarily responsible for the observed inverse correlation between apo(a) isoform size and Lp(a) levels, with a contribution of catabolism restricted to larger Lp(a) isoforms.Factors that affect apoB-100 secretion from hepatocytes also affect apo(a) secretion.The identification of key hepatic receptors involved in Lp(a) clearance in vivo remains unclear, with a role for the LDL receptor seemingly restricted to conditions wherein LDL concentrations are low, Lp(a) is highly elevated and LDL receptor number is maximally upregulated.

SUMMARY

The key role for production rate of Lp(a) [including secretion and assembly of the Lp(a) particle] rather than its catabolic rate suggests that the most fruitful therapies for Lp(a) reduction should focus on approaches that inhibit production of the particle rather than its removal from circulation.

Lipoprotein(a) beyond the kringle IV repeat polymorphism: The complexity of genetic variation in the LPA gene

High lipoprotein(a) [Lp(a)] concentrations are one of the most important genetically determined risk factors for cardiovascular disease. Lp(a) concentrations are an enigmatic trait largely controlled by one single gene (LPA) that contains a complex interplay of several genetic elements with many surprising effects discussed in this review. A hypervariable coding copy number variation (the kringle IV type-2 repeat, KIV-2) generates >40 apolipoprotein(a) protein isoforms and determines the median Lp(a) concentrations. Carriers of small isoforms with up to 22 kringle IV domains have median Lp(a) concentrations up to 5 times higher than those with large isoforms (>22 kringle IV domains). The effect of the apo(a) isoforms are, however, modified by many functional single nucleotide polymorphisms (SNPs) distributed over the complete range of allele frequencies (<0.1% to >20%) with very pronounced effects on Lp(a) concentrations. A complex interaction is present between the apo (a) isoforms and LPA SNPs, with isoforms partially masking the effect of functional SNPs and, vice versa, SNPs lowering the Lp(a) concentrations of affected isoforms. This picture is further complicated by SNP-SNP interactions, a poorly understood role of other polymorphisms such as short tandem repeats and linkage structures that are poorly captured by common R² values. A further layer of complexity derives from recent findings that several functional SNPs are located in the KIV-2 repeat and are thus not accessible to conventional sequencing and genotyping technologies. A critical impact of the ancestry on correlation structures and baseline Lp(a) values becomes increasingly evident.

This review provides a comprehensive overview on the complex genetic architecture of the Lp(a) concentrations in plasma, a field that has made tremendous progress with the introduction of new technologies. Understanding the genetics of Lp(a) might be a key to many mysteries of Lp(a) and booster new ideas on the metabolism of Lp(a) and possible interventional targets.

Surgery-Induced Weight Loss and Changes in Hormonally Active Fibroblast Growth Factors: a Systematic Review and Meta-Analysis

This systematic review and meta-analysis was performed to investigate the possible changes of FGF-19 and FGF-21 after bariatric surgery (BS). Electronic databases including PubMed and Scopus were systematically searched up to February 2020 to identify pertinent studies. A total of 25 different studies were included. The overall pooled analysis identified that BS caused a significant increase in FGF-19, but had no significant effect on FGF-21. For FGF-19, this finding was supported in the subgroup analyses. For FGF-21, Roux-en-Y gastric bypass (RYGB) surgery significantly increased FGF-21 levels, whereas, in studies with follow-up duration ≥ 1 year, FGF-21 levels decreased significantly. BS reduces circulating concentration of FGF-19, but might increase FGF-21 after RYGB or decrease FGF-21 after ≥ 1 year.

Association of serum fibroblast growth factor 19 levels with arteriosclerosis parameters assessed by arterial stiffness and atherogenic index of plasma in patients with type 2 diabetes

BACKGROUND

The role of serum fibroblast growth factor 19 (FGF19) in arteriosclerosis is not well known. In the present study, we aimed to explore whether serum FGF19 levels were related to arteriosclerosis parameters, including arterial stiffness and atherogenic index of plasma (AIP), in patients with type 2 diabetes (T2D).

METHODS

A total of 200 patients with type 2 diabetes and 50 healthy controls were recruited for this study from Apr 2017 to Oct 2018. Serum FGF19 levels, arterial stiffness assessed by brachial ankle pulse wave velocity (baPWV), and AIP assessed by the triglyceride to high-density lipoprotein cholesterol (TG/HDL-c) ratio were measured in those subjects. In addition, other relevant clinical data were also collected.

RESULTS

Serum FGF19 levels in T2D patients were significantly lower than those in healthy controls (p < 0.05). The arteriosclerosis parameters, including baPWV and AIP, significantly decreased across ascending tertiles of serum FGF19 levels (all p for trend < 0.001). Moreover, the baPWV and AIP were all inversely correlated with serum FGF19 levels (r = - 0.351 and - 0.303, respectively, p < 0.001). Furthermore, after adjusting for other clinical covariates by multiple linear regression analyses, the serum FGF19 levels were independently associated with baPWV (β = - 0.20, t = - 2.23, p = 0.029) and AIP (β = - 0.28, t = - 2.66, p = 0.010).

CONCLUSIONS

The serum FGF19 levels were independently and inversely associated with baPWV and AIP, which indicate that serum FGF19 may have a protective role in atherosclerosis in patients with T2D.

A Prospective Randomized Controlled Trial of the Metabolic Effects of Sleeve Gastrectomy with Transit Bipartition

PURPOSE

To compare the effects of the sleeve gastrectomy with transit bipartition (SG + TB) procedure with standard medical therapy (SMT) in mildly obese patients with type II diabetes (T2D).

METHODS

This is a prospective, randomized, controlled trial. Twenty male adults, ≤ 65 years old, with T2D, body mass index (BMI) > 28 kg/m² and < 35 kg/m², and HbA1c level > 8% were randomized to SG + TB or to SMT. Outcomes were the remission in the metabolic and cardiovascular risk variables up to 24 months.

RESULTS

At 24 months, SG + TB group showed a significant decrease in HbaA1c values (9.3 ± 2.1 versus 5.5 ± 1.1%, P = < 0.05) whereas SMT group maintained similar levels from baseline (8.0 ± 1.5 versus 8.3 ± 1.1%, P = NS). BMI values were lower in the SG + TB group (25.3 ± 2.8 kg/m² versus 30.9 ± 2.5 kg/m²; P = < 0.001). At 24 months, none patient in SG + TB group needed medications for hyperlipidemia/hypertension. HDL-cholesterol levels increased in the SG + TB group (33 ± 8 to 45 ± 15 mg/dL, P < 0.001). After 24 months, the area under the curve (AUC) of GLP1 increased and in the SG + TB group and the AUC of the GIP concentrations was lower in the SG + TB group than in the SMT. At 3 months, SG + TB group showed a marked increase in FGF19 levels (74.1 ± 45.8 to 237.3 ± 234 pg/mL; P = 0.001).

CONCLUSIONS

SG + TB is superior to SMT and was associated with a better metabolic and cardiovascular profile.

Lipoprotein(a) Change After Sleeve Gastrectomy Is Affected by the Presence of Metabolic Syndrome

BACKGROUND

Patients with metabolic syndrome (MetS) are at high risk of developing cardiovascular disease (CVD) and lipoprotein(a) (Lp(a)) is an independent risk factor for CVD. This study aimed to determine the effect of vertical sleeve gastrectomy (VSG)-induced weight loss on Lp(a) levels in obese individuals.

METHODS

Patients submitted to VSG from January 2011 to July 2015 were included. Anthropometric and metabolic parameters were recorded before and 12 months after surgery. Univariate analysis identified associations between Lp(a) and anthropometry and metabolic parameters, and the logistic regression predictors of Lp(a) decrease after VSG.

RESULTS

MetS was present in 47% of the 330 patients involved. Patients with MetS had higher body mass index (BMI) and triglyceride levels and were more insulin-resistant. No differences were found between groups respecting Lp(a) levels prior to surgery (15.2 mg/dL vs. 15.0 mg/dL, p = 0.795). After surgery, patients without MetS had a decrease in Lp(a) levels (14.7 mg/dL vs. 12.3 mg/dL, p = 0.006), while MetS patients showed no differences (13.9 mg/dL vs. 14.6 mg/dL, p = 0.302). The regression model evidenced that older age and Δ HDL-c were predictors of Lp(a) decrease, whereas the greater the number of MetS components and lower estimated BF% loss, the lesser odds of decreasing Lp(a) after surgery.

CONCLUSIONS

Despite a global improvement of conventional CVD risk factors, only individuals without MetS showed a decrease of Lp(a) levels after VSG. Further studies should explore not only the pathophysiological mechanisms underlying the absence of decrease of Lp(a) levels in MetS patients, but also its impact on the metabolic beneficial changes usually observed after VSG.

New Frontiers in Lp(a)-Targeted Therapies

Interest in lipoprotein (a) [Lp(a)] has exploded over the past decade with the emergence of genetic and epidemiological studies pinpointing elevated levels of this unique lipoprotein as a causal risk factor for atherosclerotic cardiovascular disease (ASCVD) and calcific aortic valve disease (CAVD). This review summarizes the most recent discoveries regarding therapeutic approaches to lower Lp(a) and presents these findings in the context of an emerging, although far from complete, understanding of the biosynthesis and catabolism of Lp(a). Application of Lp(a)-specific lowering agents to outcome trials will be the key to opening this new frontier in the battle against CVD.

Pharmacological Applications of Bile Acids and Their Derivatives in the Treatment of Metabolic Syndrome

Apart from well-known functions of bile acids in digestion and solubilization of lipophilic nutrients and drugs in the small intestine, the emerging evidence from the past two decades identified the role of bile acids as signaling, endocrine molecules that regulate the glucose, lipid, and energy metabolism through complex and intertwined pathways that are largely mediated by activation of nuclear receptor farnesoid X receptor (FXR) and cell surface G protein-coupled receptor 1, TGR5 (also known as GPBAR1). Interactions of bile acids with the gut microbiota that result in the altered composition of circulating and intestinal bile acids pool, gut microbiota composition and modified signaling pathways, are further extending the complexity of biological functions of these steroid derivatives. Thus, bile acids signaling pathways have become attractive targets for the treatment of various metabolic diseases and metabolic syndrome opening the new potential avenue in their treatment. In addition, there is a significant effort to unveil some specific properties of bile acids relevant to their intrinsic potency and selectivity for particular receptors and to design novel modulators of these receptors with improved pharmacokinetic and pharmacodynamic profiles. This resulted in synthesis of few semi-synthetic bile acids derivatives such as 6α-ethyl-chenodeoxycholic acid (obeticholic acid, OCA), norursodeoxycholic acid (norUDCA), and 12-monoketocholic acid (12-MKC) that are proven to have positive effect in metabolic and hepato-biliary disorders. This review presents an overview of the current knowledge related to bile acids implications in glucose, lipid and energy metabolism, as well as a potential application of bile acids in metabolic syndrome treatment with future perspectives.

Fibroblast Growth Factor 15/19: From Basic Functions to Therapeutic Perspectives

Discovered 20 years ago, fibroblast growth factor (FGF)19, and its mouse ortholog FGF15, were the first members of a new subfamily of FGFs able to act as hormones. During fetal life, FGF15/19 is involved in organogenesis, affecting the development of the ear, eye, heart, and brain. At adulthood, FGF15/19 is mainly produced by the ileum, acting on the liver to repress hepatic bile acid synthesis and promote postprandial nutrient partitioning. In rodents, pharmacologic doses of FGF19 induce the same antiobesity and antidiabetic actions as FGF21, with these metabolic effects being partly mediated by the brain. However, activation of hepatocyte proliferation by FGF19 has long been a challenge to its therapeutic use. Recently, genetic reengineering of the molecule has resolved this issue. Despite a global overlap in expression pattern and function, murine FGF15 and human FGF19 exhibit several differences in terms of regulation, molecular structure, signaling, and biological properties. As most of the knowledge originates from the use of FGF19 in murine models, differences between mice and humans in the biology of FGF15/19 have to be considered for a successful translation from bench to bedside. This review summarizes the basic knowledge concerning FGF15/19 in mice and humans, with a special focus on regulation of production, morphogenic properties, hepatocyte growth, bile acid homeostasis, as well as actions on glucose, lipid, and energy homeostasis. Moreover, implications and therapeutic perspectives concerning FGF19 in human diseases (including obesity, type 2 diabetes, hepatic steatosis, biliary disorders, and cancer) are also discussed.

Is Lp(a) ready for prime time use in the clinic? A pros-and-cons debate

Lipoprotein (a) (Lp(a)) is a cholesterol-rich lipoprotein known since 1963. In spite of extensive research on Lp(a), there are still numerous gaps in our knowledge relating to its function, biosynthesis and catabolism. One reason for this might be that apo(a), the characteristic glycoprotein of Lp(a), is expressed only in primates. Results from experiments using transgenic animals therefore may need verification in humans. Studies on Lp(a) are also handicapped by the great number of isoforms of apo(a) and the heterogeneity of apo(a)-containing fractions in plasma. Quantification of Lp(a) in the clinical laboratory for a long time has not been standardized. Starting from its discovery, reports accumulated that Lp(a) contributed to the risk of cardiovascular disease (CVD), myocardial infarction (MI) and stroke. Early reports were based on case control studies but in the last decades a great deal of prospective studies have been published that highlight the increased risk for CVD and MI in patients with elevated Lp(a). Final answers to the question of whether Lp(a) is ready for wider clinical use will come from intervention studies with novel selective Lp(a) lowering medications that are currently underway. This article expounds arguments for and against this proposition from currently available data.

Diallyl disulphide inhibits apolipoprotein(a) expression in HepG2 cells through the MEK1-ERK1/2-ELK-1 pathway

Background

Lipoprotein(a) [LP(a)] is implicated as a common and independent risk factor for cardiovascular diseases. The therapeutic options currently available for reducing plasma LP(a) concentrations are limited. Diallyl disulphide (DADS), the main component of garlic, regulates lipid metabolism in hepatocytes and adipocytes through ERK1/2 signalling. This study aimed to assess the effect of DADS on apolipoprotein(a) [apo(a)] in HepG2 cells. We also determined the effects of DADS on apo(a) expression and secretion in HepG2 cells as well as the underlying mechanisms.

Methods

We examined the role of DADS on apo(a) expression in HepG2 cells by treating cell with different concentrations of DADS (10, 20, 40 and 80 μg/mL) for 24 h or treating cells with 40 μg/mL DADS for 0, 6, 12, 24 and 48 h. Then we used quantitative real-time PCR to analysis apo(a) mRNA levels, used Western blot to analysis apo(a) protein levels and used enzyme-linked immunosorbent assay to test apo(a) secreted levels. To farther determined the role of DADS, we applied Transfection of small interfering RNA to knockdown ELK-1levels and applied PD98059, a specific inhibitor of ERK1/2, to block ERK1/2 signal.

Results

The results show DADS inhibited apo(a) at both the mRNA and protein levels in HepG2 cells in a dose-dependent manner. DADS-mediated inhibition of apoa(a) expression in HepG2 cells was attenuated when the cells were cultured in medium containing PD98059 (ERK1/2 inhibitor) or were transfected with siRNAs against MEK1 or ELK-1. Overexpression of apo(a) yielded similar results.

Conclusions

This study reveals that DADS can downregulate apo(a) expression in a dose-dependent manner via the MEK-ERK12-ELK-1 pathway.

Bile Acid Control of Metabolism and Inflammation in Obesity, Type 2 Diabetes, Dyslipidemia, and Nonalcoholic Fatty Liver Disease

Bile acids are signaling molecules that coordinately regulate metabolism and inflammation via the nuclear farnesoid X receptor (FXR) and the Takeda G protein-coupled receptor 5 (TGR5). These receptors activate transcriptional networks and signaling cascades controlling the expression and activity of genes involved in bile acid, lipid and carbohydrate metabolism, energy expenditure, and inflammation by acting predominantly in enterohepatic tissues, but also in peripheral organs. In this review, we discuss the most recent findings on the inter-organ signaling and interplay with the gut microbiota of bile acids and their receptors in meta-inflammation, with a focus on their pathophysiologic roles in obesity, type 2 diabetes, dyslipidemia, and nonalcoholic steatohepatitis, and their potential therapeutic applications.

Vitamin C down-regulate apo(a) expression via Tet2-dependent DNA demethylation in HepG2 cells

Lipoprotein(a)[Lp(a)] is a risk factor for coronary heart diseases. However, the metabolism of this protein remains poorly understood. Efficient and specific drugs that can decrease high plasma levels of Lp(a) have not been developed yet. Vitamin C is responsible for maintaining the catalytic activity of a group of iron and 2-oxoglutarate (2OG)-dependent dioxygenases and induces the generation of 5-hydroxymethylcytosine (5hmC) via Ten-eleven translocation (Tet) dioxygenases. In addition, It has been reported vitamin C deficiency induces atherosclerosis and increases Lp(a) and apo(a) plasma levels in Lp(a)+ mice. However, the mechanism is still unclear. In this study, we investigated the effects of vitamin C on apo(a) expression and the possible molecular mechanism of vitamin C that influences apolipoprotein(a) [apo(a)] biosynthesis in HepG2 cells. Results showed that vitamin C significantly inhibited the expression and secretion levels of apo(a). Vitamin C can also increase ELK1 expression and hydroxymethylation of ELK1 promoter and the globle DNA in HepG2 cells. In addition, the effects of vitamin C inhibiting the apo(a) expression were attenuated by ELK1siRNA and Tet2siRNA. These results suggested vitamin C down-regulate apo(a) expression via Tet2-dependent DNA demethylation in HepG2 cells.

Comparison of the effects of fibrates versus statins on plasma lipoprotein(a) concentrations: a systematic review and meta-analysis of head-to-head randomized controlled trials

BACKGROUND

Raised plasma lipoprotein(a) (Lp(a)) concentration is an independent and causal risk factor for atherosclerotic cardiovascular disease. Several types of pharmacological approaches are under evaluation for their potential to reduce plasma Lp(a) levels. There is suggestive evidence that statins and fibrates, two frequently employed lipid-lowering drugs, can lower plasma Lp(a). The present study aims to compare the efficacy of fibrates and statins in reducing plasma concentrations of Lp(a) using a meta-analysis of randomized head-to-head trials.

METHODS

Medline and Scopus databases were searched to identify randomized head-to-head comparative trials investigating the efficacy of fibrates versus statins in reducing plasma Lp(a) levels. Meta-analysis was performed using a random-effects model, with inverse variance weighted mean differences (WMDs) and 95% confidence intervals (CIs) as summary statistics. The impact of putative confounders on the estimated effect size was explored using random effects meta-regression.

RESULTS

Sixteen head-to-head comparative trials with a total of 1388 subjects met the eligibility criteria and were selected for this meta-analysis. Meta-analysis revealed a significantly greater effect of fibrates versus statins in reducing plasma Lp(a) concentrations (WMD, -2.70 mg/dL; 95% CI, -4.56 to -0.84; P = 0.004). Combination therapy with fibrates and statins had a significantly greater effect compared with statin monotherapy (WMD, -1.60 mg/dL; 95% CI, -2.93 to -0.26; P = 0.019) but not fibrate monotherapy (WMD, -1.76 mg/dL; 95% CI, -5.44 to +1.92; P = 0.349) in reducing plasma Lp(a) concentrations. The impact of fibrates versus statins in reducing plasma Lp(a) concentrations was not found to be significantly associated with treatment duration (P = 0.788).

CONCLUSIONS

Fibrates have a significantly greater effect in reducing plasma Lp(a) concentrations than statins. Addition of fibrates to statins can enhance the Lp(a)-lowering effect of statins.

Human Genetics and the Causal Role of Lipoprotein(a) for Various Diseases

Lipoprotein(a) [Lp(a)] is a highly atherogenic lipoprotein that is under strong genetic control by the LPA gene locus. Genetic variants including a highly polymorphic copy number variation of the so called kringle IV repeats at this locus have a pronounced influence on Lp(a) concentrations. High concentrations of Lp(a) as well as genetic variants which are associated with high Lp(a) concentrations are both associated with cardiovascular disease which very strongly supports causality between Lp(a) concetrations and cardiovascular disease. This method of using a genetic variant that has a pronounced influence on a biomarker to support causality with an outcome is called Mendelian randomization approach and was applied for the first time two decades ago with data from Lp(a) and cardiovascular disease. This approach was also used to demonstrate a causal association between high Lp(a) concentrations and aortic valve stenosis, between low concentrations and type-2 diabetes mellitus and to exclude a causal association between Lp(a) concentrations and venous thrombosis. Considering the high frequency of these genetic variants in the population makes Lp(a) the strongest genetic risk factor for cardiovascular disease identified so far. Promising drugs that lower Lp(a) are on the horizon but their efficacy in terms of reducing clinical outcomes still has to be shown.

Lipoprotein (a): a historical appraisal

Initially, lipoprotein (a) [Lp(a)] was believed to be a genetic variant of lipoprotein (Lp)-B. Because its lipid moiety is almost identical to LDL, Lp(a) has been deliberately considered to be highly atherogenic. Lp(a) was detected in 1963 by Kare Berg, and individuals who were positive for this factor were called Lpa⁺ Lpa⁺ individuals were found more frequently in patients with coronary heart disease than in controls. After the introduction of quantitative methods for monitoring of Lp(a), it became apparent that Lp(a), in fact, is present in all individuals, yet to a greatly variable extent. The genetics of Lp(a) had been a mystery for a long time until Gerd Utermann discovered that apo(a) is expressed by a variety of alleles, giving rise to a unique size heterogeneity. This size heterogeneity, as well as countless mutations, is responsible for the great variability in plasma Lp(a) concentrations. Initially, we proposed to evaluate the risk of myocardial infarction at a cut-off for Lp(a) of 30-50 mg/dl, a value that still is adopted in numerous epidemiological studies. Due to new therapies that lower Lp(a) levels, there is renewed interest and still rising research activity in Lp(a). Despite all these activities, numerous gaps exist in our knowledge, especially as far as the function and metabolism of this fascinating Lp are concerned.

The re-emergence of lipoprotein(a) in a broader clinical arena

Lipoprotein(a) [Lp(a)] is a genetic, independent and likely causal risk factor for cardiovascular disease (CVD) and calcific aortic valve stenosis (CAVS). Lp(a) levels are primarily genetically determined and tend to fluctuate only mildly around a pre-determined level. In primary care settings, one Lp(a) measurement can reclassify up to 40% of patients in intermediate risk score categories. In secondary care settings, recent data from the JUPITER and AIM-HIGH trials demonstrate that elevated Lp(a) remains part of the "residual risk" despite achievement of low-density lipoprotein cholesterol levels <70 mg/dL. Recent reports suggest that statins can increase Lp(a) levels, potentially further contributing to this residual risk. Current therapies to lower Lp(a) are limited to niacin, mipomersen and proprotein convertase subtilisin kexin-type 9 inhibitors, but these drugs are limited by weak efficacy and not specifically approved for Lp(a) lowering. Emerging therapies to lower Lp(a) may shed new light into the potential clinical benefit of lowering Lp(a) in CVD and CAVS.

Evidence-based assessment of lipoprotein(a) as a risk biomarker for cardiovascular diseases - Some answers and still many questions

The present article is aimed at outlining the current state of knowledge regarding the clinical value of lipoprotein(a) (Lp(a)) as a marker of cardiovascular disease (CVD) risk by summarizing the results of recent clinical studies, meta-analyses and systematic reviews. The literature supports the predictive value of Lp(a) on CVD outcomes, although the effect size is modest. Lp(a) would also appear to have an effect on cerebrovascular outcomes, however the effect appears even smaller than that for CVD outcomes. Consideration of apolipoprotein(a) (apo(a)) isoforms and LPA genetics in relation to the simple assessment of Lp(a) concentration may enhance clinical practice in vascular medicine. We also describe recent advances in Lp(a) research (including therapies) and highlight areas where further research is needed such as the measurement of Lp(a) and its involvement in additional pathophysiological processes.

Metabolic effects of bile acid sequestration: impact on cardiovascular risk factors

PURPOSE OF REVIEW

This article discusses the impact of bile acid sequestrants (BAS) on cardiovascular risk factors (CVRFs), on the basis of recent (pre)clinical studies assessing the metabolic impact of modulation of enterohepatic bile acid signaling via the bile acid receptors farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5).

RECENT FINDINGS

BAS decrease low-density lipoprotein-cholesterol by stimulating de novo hepatic bile acid synthesis and lowering intestinal lipid absorption, and improve glucose homeostasis in type 2 diabetes mellitus, at least in part by increasing GLP-1 production, via intestinal TGR5- and FXR-dependent mechanisms. Intestinal and peripheral FXR and TGR5 modulation also affects peripheral tissues, which can contribute to the reduction of CVRFs.

SUMMARY

Bile acids are regulators of metabolism acting in an integrated interorgan manner via FXR and TGR5. Modulation of the bile acid pool size and composition, and selective interference with their receptors could, therefore, be a therapeutic approach to decrease CVRFs. Even though clinical cardiovascular outcome studies using BAS are still lacking, the existing data point to BAS as an efficacious pharmacological approach to reduce CVRFs.

Bariatric surgery, lipoprotein metabolism and cardiovascular risk

PURPOSE OF REVIEW

To summarize recent epidemiological, preclinical and clinical studies on the effects of Roux-en-Y-gastric bypass (RYGBP) surgery on cardiovascular risk factors and the underlying mechanisms.

RECENT FINDINGS

Although RYGBP has mechanical effects on the gastrointestinal tract, the reduced gastric pouch and intestinal calorie absorption cannot fully explain the metabolic improvements.

SUMMARY

Obesity predisposes to cardiovascular risk factors such as dyslipidemia, type 2 diabetes, nonalcoholic fatty liver disease and hypertension. In contrast to the limited success of pharmacological and lifestyle interventions, RYGBP induces sustained weight loss, metabolic improvements and decreases morbidity/mortality. In line, RYGBP reduces cardiovascular risk factors. Although the mechanisms are not entirely understood, RYGBP induces complex changes in the gut affecting other organs through endocrine and metabolic signals from the intestine to all key metabolic organs, which can link RYGBP and decreased cardiovascular risk. Here, we discuss the roles of changes in lipid absorption and metabolism, bile acid metabolism, gut hormones and the microbiote as potential mechanisms in the decreased cardiovascular risk and metabolic improvement after RYGBP.

Fibroblast Growth Factor Signaling in Metabolic Regulation

The prevalence of obesity is a growing health problem. Obesity is strongly associated with several comorbidities, such as non-alcoholic fatty liver disease, certain cancers, insulin resistance, and type 2 diabetes, which all reduce life expectancy and life quality. Several drugs have been put forward in order to treat these diseases, but many of them have detrimental side effects. The unexpected role of the family of fibroblast growth factors in the regulation of energy metabolism provides new approaches to the treatment of metabolic diseases and offers a valuable tool to gain more insight into metabolic regulation. The known beneficial effects of FGF19 and FGF21 on metabolism, together with recently discovered similar effects of FGF1 suggest that FGFs and their derivatives carry great potential as novel therapeutics to treat metabolic conditions. To facilitate the development of new therapies with improved targeting and minimal side effects, a better understanding of the molecular mechanism of action of FGFs is needed. In this review, we will discuss what is currently known about the physiological roles of FGF signaling in tissues important for metabolic homeostasis. In addition, we will discuss current concepts regarding their pharmacological properties and effector tissues in the context of metabolic disease. Also, the recent progress in the development of FGF variants will be reviewed. Our goal is to provide a comprehensive overview of the current concepts and consensuses regarding FGF signaling in metabolic health and disease and to provide starting points for the development of FGF-based therapies against metabolic conditions.

[Clinical significance of and treatment options for increased lipoprotein(a)]

Lipoprotein(a) has been shown to be associated with an increased incidence of cardiovascular diseases for decades. However, only recent research revealed more about its physiological function and its role in the development of cardiovascular diseases. The authors summarize the physiological role of lipoprotein(a), causes and treatment of elevated lipoprotein(a) level, and the association between lipoprotein(a) and cardiovascular diseases.

Lipoprotein(a) as a therapeutic target in cardiovascular disease

INTRODUCTION

Recent advances in genetics and epidemiology have once again thrust lipoprotein(a) (Lp(a)) into the clinical spotlight. Elevated plasma concentrations of Lp(a) are an independent, causal risk factor for coronary heart disease. The mechanisms underlying the pathogenicity of Lp(a) remain obscure, and uncertainty continues to surround the appropriate use of Lp(a) in the clinic.

AREAS COVERED

We summarize the most recent findings on the biology and epidemiology of Lp(a), and use this as a platform to discuss strategies to lower plasma Lp(a) concentrations. The majority of the existing approaches are not Lp(a) specific since they also improve other aspects of the lipid profile. It is possible, however, that the unique characteristics of Lp(a) can be exploited to design therapeutics to specifically lower Lp(a).

EXPERT OPINION

Lp(a) should be measured in selected patients, including those with a family history of cardiovascular disease (CVD), those with several risk factors for CVD and those who exhibit resistance to statins. Lp(a) lowering should not be the primary driver of choice of therapy, as it has not yet been established through randomized controlled trials that Lp(a) lowering per se has clinical benefit. The development of agents that specifically lower Lp(a) will allow interrogation of this question.

Update on lipoprotein(a) as a cardiovascular risk factor and mediator

Recent genetic studies have put the spotlight back onto lipoprotein(a) [Lp(a)] as a causal risk factor for coronary heart disease. However, there remain significant gaps in our knowledge with respect to how the Lp(a) particle is assembled, the route of its catabolism, and the mechanism(s) of Lp(a) pathogenicity. It has long been speculated that the effects of Lp(a) in the vasculature can be attributed to both its low-density lipoprotein moiety and the unique apolipoprotein(a) component, which is strikingly similar to the kringle-containing fibrinolytic zymogen plasminogen. However, the ability of Lp(a) to modulate either purely thrombotic or purely atherothrombotic processes in vivo remains unclear. The presence of oxidized phospholipid on Lp(a) may underlie many of the proatherosclerotic effects of Lp(a) that have been identified both in cell models and in animal models, and provides a possible avenue for identifying therapeutics aimed at mitigating the effects of Lp(a) in the vasculature. However, the beneficial effects of targeted Lp(a) therapeutics, designed to either lower Lp(a) concentrations or interfere with its effects, on cardiovascular outcomes remains to be determined.

When should we measure lipoprotein (a)?

Recently published epidemiological and genetic studies strongly suggest a causal relationship of elevated concentrations of lipoprotein (a) [Lp(a)] with cardiovascular disease (CVD), independent of low-density lipoproteins (LDLs), reduced high density lipoproteins (HDL), and other traditional CVD risk factors. The atherogenicity of Lp(a) at a molecular and cellular level is caused by interference with the fibrinolytic system, the affinity to secretory phospholipase A2, the interaction with extracellular matrix glycoproteins, and the binding to scavenger receptors on macrophages. Lipoprotein (a) plasma concentrations correlate significantly with the synthetic rate of apo(a) and recent studies demonstrate that apo(a) expression is inhibited by ligands for farnesoid X receptor. Numerous gaps in our knowledge on Lp(a) function, biosynthesis, and the site of catabolism still exist. Nevertheless, new classes of therapeutic agents that have a significant Lp(a)-lowering effect such as apoB antisense oligonucleotides, microsomal triglyceride transfer protein inhibitors, cholesterol ester transfer protein inhibitors, and PCSK-9 inhibitors are currently in trials. Consensus reports of scientific societies are still prudent in recommending the measurement of Lp(a) routinely for assessing CVD risk. This is mainly caused by the lack of definite intervention studies demonstrating that lowering Lp(a) reduces hard CVD endpoints, a lack of effective medications for lowering Lp(a), the highly variable Lp(a) concentrations among different ethnic groups and the challenges associated with Lp(a) measurement. Here, we present our view on when to measure Lp(a) and how to deal with elevated Lp(a) levels in moderate and high-risk individuals.

Lipoprotein(a) metabolism: potential sites for therapeutic targets

Lipoprotein(a) [Lp(a)] resembles low-density lipoprotein (LDL), with an LDL lipid core and apolipoprotein B (apoB), but contains a unique apolipoprotein, apo(a). Elevated Lp(a) is an independent risk factor for coronary and peripheral vascular diseases. The size and concentration of plasma Lp(a) are related to the synthetic rate, not the catabolic rate, and are highly variable with small isoforms associated with high concentrations and pathogenic risk. Apo(a) is synthesized in the liver, although assembly of apo(a) and LDL may occur in the hepatocytes or plasma. While the uptake and clearance site of Lp(a) is poorly delineated, the kidney is the site of apo(a) fragment excretion. The structure of apo(a) has high homology to plasminogen, the zymogen for plasmin and the primary clot lysis enzyme. Apo(a) interferes with plasminogen binding to C-terminal lysines of cell surface and extracellular matrix proteins. Lp(a) and apo(a) inhibit fibrinolysis and accumulate in the vascular wall in atherosclerotic lesions. The pathogenic role of Lp(a) is not known. Small isoforms and high concentrations of Lp(a) are found in healthy octogenarians that suggest Lp(a) may also have a physiological role. Studies of Lp(a) function have been limited since it is not found in commonly studied small mammals. An important aspect of Lp(a) metabolism is the modification of circulating Lp(a), which has the potential to alter the functions of Lp(a). There are no therapeutic drugs that selectively target elevated Lp(a), but a number of possible agents are being considered. Recently, new modifiers of apo(a) synthesis have been identified. This review reports the regulation of Lp(a) metabolism and potential sites for therapeutic targets.

Lipoprotein(a): resurrected by genetics

Plasma lipoprotein(a) [Lp(a)] is a quantitative genetic trait with a very broad and skewed distribution, which is largely controlled by genetic variants at the LPA locus on chromosome 6q27. Based on genetic evidence provided by studies conducted over the last two decades, Lp(a) is currently considered to be the strongest genetic risk factor for coronary heart disease (CHD). The copy number variation of kringle IV in the LPA gene has been strongly associated with both Lp(a) levels in plasma and risk of CHD, thereby fulfilling the main criterion for causality in a Mendelian randomization approach. Alleles with a low kringle IV copy number that together have a population frequency of 25-35% are associated with a doubling of the relative risk for outcomes, which is exceptional in the field of complex genetic phenotypes. The recently identified binding of oxidized phospholipids to Lp(a) is considered as one of the possible mechanisms that may explain the pathogenicity of Lp(a). Drugs that have been shown to lower Lp(a) have pleiotropic effects on other CHD risk factors, and an improvement of cardiovascular endpoints is up to now lacking. However, it has been established in a proof of principle study that lowering of very high Lp(a) by apheresis in high-risk patients with already maximally reduced low-density lipoprotein cholesterol levels can dramatically reduce major coronary events.

Emerging therapeutic agents to lower lipoprotein (a) levels

PURPOSE OF REVIEW

Recent epidemiological and genetic studies have suggested that lipoprotein (a) [Lp(a)] is a causal mediator of cardiovascular disease (CVD). There is now interest in evaluating Lp(a) as a therapeutic target. This review will summarize emerging therapeutic agents to lower Lp(a).

RECENT FINDINGS

Apheresis is the most efficacious method to lower Lp(a). Currently, there are no approved drugs to specifically lower Lp(a). However, recent data has demonstrated that Lp(a) can be significantly lowered, along with reductions in other apolipoprotein B-100 (apoB) containing lipoproteins, with antisense oligonucleotides to apoB, monoclonal antibodies to proprotein convertase subtilisin/kexin type 9, cholesterol ester transfer protein inhibitors, and thyromimetics. The farnesoid X receptor/fibroblast growth factor axis and interleukin-6 also influence Lp(a) levels and may be targets of therapy. Finally, specific apolipoprotein (a) [apo(a)] inhibitors apo(a) have been developed and reduce apo(a) mRNA and protein levels up to 86% without significantly affecting other lipoproteins.

SUMMARY

Lp(a) remains the last major lipoprotein disorder without any specific therapy. With the strong and accumulating data on its role as a causal risk factor for CVD, a rationale exists to develop novel agents to reduce Lp(a) and test the hypothesis that this will lead to reduced CVD events.

Nicotinic acid inhibits hepatic APOA gene expression: studies in humans and in transgenic mice

Elevated plasma lipoprotein(a) (LPA) levels are recognized as an independent risk factor for cardiovascular diseases. Our knowledge on LPA metabolism is incomplete, which makes it difficult to develop LPA-lowering medications. Nicotinic acid (NA) is the main drug recommended for the treatment of patients with increased plasma LPA concentrations. The mechanism of NA in lowering LPA is virtually unknown. To study this mechanism, we treated transgenic (tg) APOA mice with NA and measured plasma APOA and hepatic mRNA levels. In addition, mouse and human primary hepatocytes were incubated with NA, and the expression of APOA was followed. Feeding 1% NA reduced plasma APOA and hepatic expression of APOA in tg-APOA mice. Experiments with cultured human and mouse primary hepatocytes in addition to reporter assays performed in HepG2 cells revealed that NA suppresses APOA transcription. The region between -1446 and -857 of the human APOA promoter harboring several cAMP response element binding sites conferred the negative effect of NA. In accordance, cAMP stimulated APOA transcription, and NA reduced hepatic cAMP levels. It is suggested that cAMP signaling might be involved in reducing APOA transcription, which leads to the lowering of plasma LPA.